There are currently two methods for attaching MC armored cable into box openings. One employs existing internal/external clamps and added secondary connectors/fittings. The internal clamps usually are attached to the box by means of a threaded screw. This serves to keep the connector in place, and to compress the connector onto the cable once inserted. This is, however, a manual process, and can be difficult to thoroughly tighten down to the necessary torque. If the clamp is on the inside, knockout holes must be removed before cable insertion. Also, the protruding screw on the backside of the box might become a concern for the end user at times.
A second method is to attach a connector to the existing box. This is typically done on the outside. In most cases, this involves removing existing box knockout holes, inserting the connector, and finally inserting the cable into the connector body. Usually the inside body of the connector has teeth or fingers to grab and hold the cable in place. Removal of these systems is very difficult, due in part to the nature of the design. Most of these systems have two separate functions, the front of the connector latches to the body of the box, and independently, the teeth on the rear (usually located inside the fitting) hold the cable in place. The front latching mechanisms are typical of multi-finger designs that make it difficult to remove the connector without destroying the fingers.
For other designs, once the cable is inserted, an interference fit is created, by means of the teeth flexing towards the outer housing of the assembly. The walls of the connector wedge the outer walls of the box, internally by the cable, and externally by the box. These connectors can be removed by removing the interference, i.e., the cable body itself, from the connector. These connectors can be difficult to install while the cable is in the fitting, due to the fact that the fitting is already flared out and now must be compressed into place into the box.
Other connectors for attaching cable to a box are known. U.S. Pat. No. 2,458,409 and U.S. Pat. No. 3,858,151 and U.S. Pat. No. 4,012,578 all disclose a single piece cable connector. However, each connector must be inserted from inside the box.
U.S. Pat. No. 4,990,721 shows a one-piece connector that is inserted from outside the box. U.S. Pat. No. 6,194,661, U.S. Pat. No. 6,355,884 and U.S. Pat. No. 6,521,831 each show a duplex connector, i.e. two connectors alongside each other.